I understand people not looking at Jenny critically enough. She was abused and damaged in at least one way and obviously didn’t act rationally as a result.
As for Forrest, all he wanted was her. Yes, he would have still gone off to war like most young men at the time, but he would have taken her with him on the shrimp boat. Or abandoned that plan, if she asked. He probably wouldn’t have devoted as much time practicing ping pong and he definitely wouldn’t have been so disillusioned with the world to go running for 2 years straight.
For better or worse, Forrest focused on his pursuits and achievements, because Jenny never really accepted or chose him when she had the chance.